There are three basic prior art structures and methods for dealing with spent ribbon in a printer.
First, the ribbon is taken up onto a disposable and relatively rigid core which is mounted onto an overdrive take-up spindle in the printer. The core takes all the occurring radial loads, not transferring loads to the overdrive take-up spindle. As a result, the core with the wound up ribbon can be easily removed from the overdrive take-up spindle. The core used to take up the ribbon on the overdrive take-up spindle is pulled off of the spindle together with the spent ribbon and it also gets discarded with the ribbon. Usually, the cores used to take up spent ribbon are the same ones as the ones on which ribbon is supplied. This forces the user to meticulously keep the cores of the empty ribbon supply roll for later use as rewind cores (or to purchase spare cores). An extra supply of cores is necessary if ribbon gets changed in mid roll, e.g. to print onto wider or narrower media or onto media which requires a different kind of ribbon or to print in a different color.
Second, the ribbon comes in a cartridge which incorporates a ribbon supply spindle body and a take-up spindle body. Use of this system in some applications (usually low speed, small through put) provides ease of operation at a higher cost for ribbon (due to the cartridge).
Third, the ribbon is taken up under tension directly onto an overdrive take-up spindle. This method does not require the user to keep a supply of spare cores. The taken-up ribbon loads, however, act directly onto the take-up spindle and may make removal of the taken-up ribbon with unsuitable means difficult. At times, under a combination of worst case conditions, the user actually has to result to means like cutting through most of the taken-up ribbon windings in order to remove it from the spindle.
Prior art ribbon removal mechanisms in which the ribbon is taken up under tension directly onto an overdrive take-up spindle include hooks, or collapsing/retracting blades.
Some prior art structures use "J-hooks" or "D-hooks". In their simplest form, the J-hook is a wire bent to form the shape of a L or an J. The long arm rests in an axial groove in the outer shell of the take-up spindle. The first layer of taken-up ribbon contacts the long arm directly, or it even may be folded around that arm once prior to placing the arm into the groove to aid in starting the ribbon on the take-up roll. To remove the wound-up ribbon, the J-hook is rotated several times and is then pulled out from underneath the spent ribbon. Usually, the hook is coated with a material which reduces the coefficient of friction between the hook and the spindle body, as well as between the hook and the spent ribbon. After removing the hook, the spent ribbon can be removed from the spindle. Prior to starting to take up a new roll of ribbon, however, the J-hook must be put back into place and must be arrested in its correct position. If the user forgets to do so, this usually results in the user having to remove the taken-up ribbon by laboriously cutting it off.
Furthermore, if the hook becomes loose, the hook may get lost. This will result in down time because the user will not print until the new part is delivered and installed, or if the user prints without the hook, the user must spend otherwise productive time cutting spent ribbon off of the spindle in order to remove it therefrom.
Another version of the J-hook is shaped such that the cross section of the long arm of the wire is D-shaped, called a J-D-hook here. This long arm is positioned in an axial groove in the outer shell of the take-up spindle. The first layer of taken up ribbon contacts this long arm directly. The correct position of the J-D-hook for taking up ribbon is such that the D is upright (the flat of the D is on or parallel to a plane through the spindle axis), protruding over the outside circumference of the take-up spindle, thus lengthening the length of each taken-up winding. When the taken-up ribbon is to be removed, the J-D-hook is rotated so that the D lays flat. This releases some or all of the ribbon load onto the spindle, because the D does now not protrude (or to a lesser extent, depending on the involved geometries) over the spindle's outer circumference. If the design is such that the rotated J-D-hook is still partially protruding and a partial load is still present, the J-D-hook must be pulled out to completely relax all stored tension in the ribbon and thus to eliminate all loads onto the spindle (removable D-hook). The taken-up ribbon can then be removed from the spindle. If the user forgets to put the J-D-hook back in place correctly prior to starting new ribbon, the results are the same as above with the J-hook.
If the design is such that by rotating the J-D-hook all loads are removed, the user can remove the ribbon without first having to remove the hook, called a captured D-hook. In this design, however, the captured D-hook still has to be arrested in its correct position prior to starting to take up a new roll of ribbon or the same problems discussed above will result. Compared to the removable J-D-hook, the captured D-hook does not have removable parts, but requires more force to turn/twist (the removable J-D-hook splits the required actuation forces up in two actions: turning/twisting and removing from the spindle).
All of these hook designs have other possible modes of failure which may occur when printing with narrow ribbon, but are not restricted to that situation. Depending on conditions, these possible modes of failure are: (1) With the J-hook, failure may occur under certain circumstances: that the occurring ribbon forces are so high that the user cannot pull out the hook and the result is that the ribbon has to be cut off of the spindle. (2) With narrow ribbon, failure may occur because turning the J-D-hook at its handle at the outboard end of the spindle only accomplishes a twisting of the D-shaped portion of the hook which is not covered by ribbon (like a torsion bar), but having little or no effect on the portion at the very inboard side of the spindle which is clamped down by the ribbon. Thus, the D under the ribbon never moves (or collapses) and it is not possible to remove the ribbon without cutting it off. Depending on design and situation, a variation of this failure is that the user is simply not able to apply the required force to twist the handle. (3) If it is possible to turn the J-D-hook and to collapse the D, it may happen that the amount of load/pressure relief is not sufficient to be able to either pull the hook out (removable hook design) or to remove the ribbon (captured hook design). Again, the result is that the ribbon has to be cut off. (4) With the removable J-hook and the removable J-D-hook, failure is possible in that even if the hook can be removed and ribbon tension and forces are released as much as the design permits, that the remaining tension/forces are still too high to remove the ribbon. Again, the result is that the ribbon will have to be cut off. (5) It is easily possible that the user, in the attempt to remove the ribbon, not only breaks fingers, knuckles and fingernails, but also, especially when using tools like pliers, knives or the like, damages the printer. The user may also push or pull the printer off of a table when one hand slips (e.g. the one steadying the printer) and the other hand does not slip (e.g. the one pulling the hook or the ribbon).
As mentioned above, the other type of prior art ribbon removal mechanism uses self-resetting collapsing/retracting blades. These blades are mounted inside the ribbon take-up spindle body, but protrude over the outer circumference of the spindle body when not collapsed. In the prior art version, the actuation of the collapsing mechanism is done by pushing a knob at the outboard end of the spindle. The knob is an integral part of a plunger which is guided internally within the spindle and which supports the blades in their protruding position. Pushing the knob inwardly into the spindle body moves the surfaces which support the blades out of the way so that the blades can collapse into the space previously taken up by the support geometry on the plunger within the spindle body. Once the ribbon is removed from the spindle, the plunger, actuated by a single return spring, pushes with its integral wedge surfaces the blades back out to their protruding position to self-reset the mechanism.
If it is possible to push the knob in to activate the plunger, the blades will collapse and this mechanism works quite well to allow the ribbon to be removed. The self-resetting of the mechanism also works well if the knob can be pushed inward to activate the plunger. It has been found, however, that it is not always possible to push the knob inwardly because of the design and because of the occurring ribbon loads, as well as other circumstances. As a result, the user either has to fall back on the usage of tools, for example a hammer, to push the knob inwardly (which is not advisable and also does not always suffice), or the user has to cut the ribbon off of the ribbon take-up spindle.
In this prior art ribbon removal mechanism, the failure is explainable as one of two possibilities, both of which are remedied by the present invention.
First, the loads are so high that the knob/plunger cannot be moved with acceptable actuation force. It is thought that the pressure per surface area may exceed the permissible material limit and the contact surfaces dimple or otherwise deform. This deformation locally causes some form-fit of the ribbon onto the blades. The actuation force must be high enough to overcome this deformation.
It is also thought that the forces to move the plunger are too high simply because the occurring ribbon forces are too high and/or because the coefficient of friction is too high. The flat support surfaces in the prior art system do not provide a mechanical advantage to reduce the actuation forces. The only way to lower actuation forces is by reducing the coefficient of friction. The present invention provides a significant improvement because the members always rest on angled surfaces, thus permanently predisposing the sliding of the blades on the support members. In the present invention, the blades are prevented from sliding on the support members because a wedge angle is chosen such that under the occurring coefficient of friction (and under the influence of the return spring), the sliding will not happen until the knob is pushed inwardly. The difference between resting on that angled surface in the present invention and on a flat surface as in the prior art, however, is what contributes to the reduction in actuation force.
Second, the loads are very high, but the knob/plunger is actually movable (whether that is with an acceptable force or not is debatable). The knob/plunger is only movable, however, until its position is close to where the change over from the flat support surface to the angled surface occurs. In that position, the contact surface area approaches zero and the stresses approach infinite. Thus, the material will deform (dimple) and it becomes extremely difficult to move the plunger.
The present invention presents a novel ribbon take-up spindle for a printer which overcomes the problems found in the prior art. Other features and advantages of the present invention will become apparent upon a reading of the attached specification, in combination with a study of the drawings.